Cinnabar (HgS) is a prominent ore of mercury. The number of grams of mercury present in $225\mathit{ g}$ of pure HgS are (Molar mass of Hg and S are $200.6\mathit{ g}$)

Molar mass of HgS 
$= 200.6 + 32$
$= 232.6\mathit{ g}$

$\mathrm{Mass} \mathrm{of} \mathrm{Hg} \mathrm{in} 232.6 \mathrm{g} \mathrm{of} \mathrm{HgS} =\mathrm{ }200.6 \mathrm{g}$
$\mathrm{Mass} \mathrm{of} \mathrm{Hg} \mathrm{in} 225 \mathrm{g} \mathrm{of} \mathrm{HgS}$=
 $=\frac{200.6}{232.6}\times 225$
$= 194.04\mathit{ g}$
 

So, $194.04\mathit{ g}$ of mercury are present in $225\mathit{ g}$ g of pure HgS.